The present invention generally relates to a liquid crystal display, more particularly to a thin film transistor-liquid crystal display(xe2x80x9cTFT-LCDxe2x80x9d) and method for manufacturing the same.
The active matrix type LCD employing .a thin film transistor as a means for activating and having a number of pixels, has a thin and light device size and displays excellent picture quality comparable to the Cathode Ray Tube monitor.
There are two types of active matrix LCD device depending on the location of storage electrode, i.e. the storage-on-gate type and the storage-on-common type.
At first, referring to FIG. 1, general active matrix type LCD is shown.
A gate bus line 2 and a data bus line 4 are arranged in a matrix configuration thereby defining pixel region. The gate bus line 2 includes a storage electrode 3 being extruded to an outer side of its corresponding pixel. More preferably, a storage capacitance electrode 3 is disposed at a previous pixel.
A thin film transistor 10 is disposed adjacent to an intersection of the gate bus line 2 and the data bus line 4. The thin film transistor 10 includes a gate electrode 2a being extended from the gate bus line 2 to its corresponding pixel; a channel layer 5 disposed on the gate electrode 2a; a source electrode 4a being extended from the data bus line 4 and in contact with one side of the channel layer 5; and a drain electrode 4b being contacted with the other side of the channel layer 5.
A pixel electrode 7 is made of a transparent film, for example, the ITO(indium tin oxide). Further, the pixel electrode 7 is overlapped with the storage electrode 3 thereby forming a storage capacitance Cst.
In the meantime, the constitutions of active matrix LCD of general storage-on-common type will be discussed with reference to FIG. 2.
Referring to FIG. 2, a gate bus line 2 and a data bus line 4 are arranged in the matrix configuration thereby defining pixel region. A thin film transistor 10 is disposed adjacent to an intersection of the gate bus line 2 and the data bus line 4.
A storage electrode 6 is disposed parallel with the gate bus line 2 and is formed between a pair of gate bus lines 2.
A pixel electrode 7 is made of the ITO, and is formed one per pixel. The pixel electrode 7 is overlapped with the storage electrode 6 thereby forming a storage capacitance Cst. At this time, the storage electrode 6 has a larger dimension at some region thereof that is overlapped with the pixel electrode compared to the other region that is not overlapped with the pixel electrode 7 to form an adequate amount of storage capacitance.
However, those LCD devices of storage-on-gate type and storage-on-common type have following shortcomings.
First of all, in an LCD of the storage-on-gate type, as the dimension of gate bus line 2 is increased, the RC time constant in the gate bus line 2 is increased. Accordingly, signal delay of the gate bus line 2 is increased.
On the other hand, in an LCD of the storage-on-common type, as the storage electrode 6 is disposed with a selected dimension in the pixel region, the aperture ratio is decreased. Furthermore, there is formed a region intersected by the data us line. It is also involves a risk of disconnection.
Accordingly, it is one object of the present invention to provide a TFT-LCD capable of reducing the signal delay in the gate-bus-line.
It is another object of the present invention to provide a TFT-LCD capable of improving the aperture ratio.
It is further object of the present invention to provide a TFT-LCD having enhanced storage capacitance.
To accomplish the objects of the present invention, in one aspect, the present invention provides a TFT-LCD comprising: a glass substrate; gate bus lines arranged parallel each other on the glass substrate; data bus lines disposed perpendicular to the gate bus lines thereby defining pixel region; a thin film transistor formed adjacent to each intersection of the gate bus line and the data bus line; a transparent pixel electrode being contacted with the thin film transistor and disposed at each pixel region; a transparent storage electrode formed at a bottom of the transparent pixel electrode, wherein the transparent storage electrode forms a storage capacitance together with the pixel electrode; and a common electrode line for transmitting common signal to the storage electrode.
The present invention further provides a TFT-LCD comprising: a glass substrate; gate bus lines arranged parallel each other on the glass substrate; data bus lines disposed perpendicular to the gate bus lines thereby defining pixel region; a thin film transistor formed adjacent to each intersection of the gate bus line and the data bus line; a transparent pixel electrode being contacted with the thin film transistor and disposed at each pixel region; a transparent storage electrode formed at a bottom of the transparent pixel electrode, wherein the transparent storage electrode forms a storage capacitance together with the pixel electrode; and a common electrode line for transmitting common signal to the storage electrode, wherein the storage electrode has the same size and shape with the pixel electrode, wherein the common electrode line has the minimum line width preventing signal delay.
In another aspect, the present invention provides a method comprising the steps of: depositing an opaque metal film on a glass substrate; forming gate bus lines and common electrode lines by patterning a selected portion of the opaque metal film; depositing an ITO layer on the glass substrate; forming a storage electrode by patterning a selected portion of the ITO layer so as to be contacted with the common electrode line; forming a gate insulating layer on the glass substrate in which the storage electrode is formed; and forming a pixel electrode on the gate insulating layer so that the entire pixel electrode region is overlapped with the storage electrode.
The present invention further provides a method comprising the steps of: depositing an ITO layer on a glass substrate; forming a storage electrode by patterning a selected portion of the ITO layer; depositing an opaque metal film on the glass substrate in which the ITO layer is formed; forming gate bus lines and common electrode sines by patterning a selected portion of the opaque metal film, wherein the common electrode lines are contacted with the storage electrode; forming a gate insulating layer on a resultant of the glass substrate; and forming a pixel electrode on the gate insulating layer so that the entire pixel electrode region is overlapped with the storage electrode.